Bushwheel Fork and Tail Shimmy

[Jeff Pralle]

Yep About to order a Supercub tail spring Anyone install one on a Pacer ? Does the bracket between the Fuselage and the tail spring still fit ? Or do I need a different Bracket ?

Thanks For your help

Question I have not seen addressed is what size main tires? This is about 3 point geometry to maintan 3-5° postive caster angle at GROSS WT.

THE SUPER CUB AND PAWNEE SPRINGS FIT. HOWEVER THE ANGLE/arch is still off even on 31” ABW.

Many of us here are making owner fabricated parts or running experimental springs to get what we need. Steeper arch and correct shock absorption with a thicker spring to help prevent breakage in the bush.

tightening the steering springs does not help. They should be almost loose. You steer with your rudder not your tail wheel. I also use the short pawl allowing more rudder travel before the tailwheel interferes, and run the 2 bolt swivel head.

this is normally a geometry issue that is nearly impossible to fix with the factory avaiable off the shelf tailsprings. The spring on the bottom design/shape was developed by an Alaska Maule pilot with 9000 hours on the same aircraft doing off airport bush ops. The right one has been lightened up and steepened for the smaller lighter Pipers.

hope this helps. PM me if you want more info.

Happy Landings!

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[Jeff Pralle]

I also run 5 coil springs in the head with the big tailwheel.

I have a ABI bushwheel assembly on a customers super cub giving the weak detent issue right now. Brand new assembly. Mentioned it at Reeves in ANC and immediate answer is maybe the flat compression spring is uneven tension...like the same problem has come up in the recent past?

might try replacing or flipping the compression spring to see if it helps.

[Steve Pierce]

Question I have not seen addressed is what size main tires? This is about 3 point geometry to maintan 3-5° postive caster angle at GROSS WT.

I had the same question, see post 7 and 8 in this thread.

[sierrasplitter]

Im running 26 inch mains. It could be caster angle and that will be re-visited. I also came across another Scott Bulletin addressing that . Scott says minimum angle should be 5-7 degrees at rest and at least zero angle when fully loaded

And yes, It could be my landing technique . This all started when I went for the bigger bushwheel tail wheel so Im still trying to track all the issues down

[Jeff Pralle]

I had a customer develop a shimmy issue ABW baby bushwheel TW after annual this winter. Part of the annual was going from 31 inch bush wheels to Landis GLH 3000 wheel skis with 800-6 tires. This alone changes the three point geometry dramatically. I found another problem where a previous install had used PA 18 shock struts, aircraft is STC approved for PA 18 gear, instead of the Pa 12 shock struts which are substantially longer. This moved the gear in closer under the fuselage elevating the front of the aircraft even more. He proceeded to make 25 or 30 over a couple of days and wore out the steering arm and the compression spring more than $300 in parts and labor.

When I have placed a camera on the tail wheel during shimmy it is often doing a full 360 not just wobbling. This is very hard of the tail wheel swivel. If you have made quite a few landings with the shimmy you may have issues with your tail wheel steering arm. Check to see that the detent notches in the arm are not rounded out, the flat compression spring is not showing wear at the pawl contact and thattge pawl is not rounded.

On a sidenote depending on when your tail wheel swivel from Bush Wheels was manufactured or if your steering arm came from Alaska Bush wheels the early ones were not heat treated and were soft they did not last very long. I’ve seen them completely worn out in less than 250 hours on a super cub. They have corrected this and are currently heat treating the steering arms. If heat treated it should be stamped HT.

[Steve Pierce]

On a sidenote depending on when your tail wheel swivel from Bush Wheels was manufactured or if your steering arm came from Alaska Bush wheels the early ones were not heat treated and were soft they did not last very long. I’ve seen them completely worn out in less than 250 hours on a super cub. They have corrected this and are currently heat treating the steering arms. If heat treated it should be stamped HT.

What is the time frame on this? Reason I ask is when Bushwheel was in Oregon I had a conversation about the heat treat process of these parts with then owner Bill Duncan.

[Jeff Pralle]

Sorry steve tried reply earlier I guess it did not go through. It has been within the last year. I was getting parts at Reeve and Gabe saw steering arm on my list asked which one. I told him I preferred the Univair since they lasted a lot longer. He told me ABW was heat treating now. So far they are holding up.

[Steve Pierce]

They have always been heat treated. There is a stamped "HT" on the steering arm indicating so.

[sierrasplitter]

the flat compression spring is not showing wear at the pawl contact

I took a very close look at this spring when I tore mine down. I can see a mark on each side that looks like it was stamped into the spring or a"notch" where the pawl would hit. It doesnt look like wear as it seems the be perfectly square and even on both sides. Can someone verify they are straight across on the edges or am I seeing a dent
Sorry, I wish I had taken a picture of the new one
I do have a pic of the one taken off the smaller stock 3200 fork that I replaced. It didnt shimmy
The indention can be see on this one between those wear marks

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[Gilbert Pierce]

When I had a problem with the tailwheel unlocking prematurely it wasn’t the spring, it was worn notches in the steering arm where the flat spring ends lock the arm.